It is well known in the art that polyurethane scrap can be converted into a crude liquid polyol product via glycolysis. Representative of the glycolysis technology are U.S. Pat. Nos. 2,937,151; 3,708,440; 3,738,946; 3,983,087; 4,044,046 and 4,110,266. Glycolysis is essentially an equilibration of the urethane, urea and isocyanurate bonds in polyurethane material with glycols, such as propylene glycol diethylene glycol and dipropylene glycol, in the presence of catalysts, such as potassium acetate and tin carboxylates, to form a crude liquid polyol product. The process is typically conducted between 180.degree. and 220.degree. C. at atmospheric pressure requiring 2 to 6 hours to reach equilibrium. The glycolysis product contains active hydroxyls from the glycols and the liberated polyols as well as oligoineric amines and aromatic diamines such as toluene diamine (TDA) and methylene dianiline (MDA).
The crude glycolysis polyol is suitable as a partial replacement for virgin polyols which are used in the manufacture of polyurethane foams and other polyurethane products. However, the crude glycolysis polyol product has limitations when used as a replacement for virgin polyols. A crude glycolysis polyol product has a very high reactivity making it difficult to control when reacted at high levels with isocyanates to generate a polyurethane foam or a polyurethane article.
In addition, the crude glycolysis polyol product has high aromatic diamine content generally greater than 1%. Since aromatic diamines such as TDA and MDA are considered suspect carcinogens, this may limit the general use of crude glycolysis polyols.
Nevertheless, there are certain advantages that the crude glycolysis polyol imparts to polyurethane articles when compared to virgin polyols. For example, in certain foam systems the glycolysis polyol increases the compression strength of the foam while at the same time reducing the foam density. The crude glycolysis polyol acts as a crosslinker in the polyurethane article and thus offers a clear advantage when used in certain polyurethane systems.
The high reactivity, the high aromatic diamine content and the improved physical properties which the crude glycolysis polyol imparts to polyurethane articles are caused by the presence of high levels of aromatic primary amines fanned during the glycolysis process. Thus, there is a need to modify the crude glycolysis polyol to reduce the reactivity and the aromatic diamine content while maintaining the improved physical properties which the glycolysis polyol can impart to polyurethane articles.
U.S. Pat. No. 4,110,266 discloses a process for decomposing polyurethane using glycols, polyols, amines and/or ammonia and converting the decomposition mixture into a product substantially free of primary and secondary amines and containing an increased amount of polyols by reacting the decomposition mixture with an excess of alkylene oxide with respect to active hydrogen atoms of the amines for a period sufficient to convert the amines to polyols and forming a product mixture substantially free of primary and secondary amines. It is preferred that more than one and up to 3 moles of alkylene oxide is employed per mole of active hydrogen atom of the amines. U.S. Pat. No. 3,983,087 discloses a process for converting scrap flexible polyurethane foam into a homogeneous mixture of polyols by heating the scrap foam with not more than its own weight of an aliphatic diol which has at least one alkyl substituent in the alkylene chain. It is also suggested (Col 4/25-33) that the hydroxyl equivalent weight of the polyol mixture obtained by the process of the invention can be modified, i.e., increased, if desired, by reacting the recovered polyol with an alkylene oxide. However, none of the examples shows such addition of an alkylene oxide to the polyol mixture.
U.S. Pat. No. 3,738,946 discloses a process for converting scrap polyurethane into a reusable polyol by heating the scrap in the presence of a dihydroxy compound consisting of (i) from 100 to 90 wt. % of an aliphatic diol having a boiling point above about 180.degree. C.; and (ii) from 0 to 10 wt. % of a dialkanol-amine having from 4 to 8 carbon atoms. When the scrap foams are derived from phosphorus containing polyols based on phosphoric acid, the polyol recovered in accordance with the process may contain significant amounts of acid-reacting material. It is recommended that the recovered polyol be treated to reduce the acid number by reacting the recovered polyol with sufficient alkylene oxide to react with all the acid hydroxyls in the recovered polyol. (Col 4/21-39). Example 7 shows the propoxylation of recovered polyol to reduce the acid number.